Seismic imaging through migration depends in part on modelling the behavior of seismic waves. The subterranean domain being imaged generally includes interfaces wherein the velocity of the seismic wave propagation changes. At such an interface with a velocity change, wave behavior depends on the incident angle. When the incident angle is less than the critical angle, part of the energy is reflected and part transmitted. At the critical angle, the transmitted wave travels parallel or along the interface. Beyond the critical angle, the energy is reflected.
Energy from waves impinging on the interface at angles greater than or equal to the critical angle can cause artifacts in the seismic image. Since the critical angle is smaller for high-contrast interfaces, this post-critical energy commonly causes artifacts at salt or carbonate boundaries or the sea-floor, for example. However, since the normal to the interface and direction of incoming waves can change rapidly, particularly for rugose interfaces, there is often a complex set of alternating pre-critical and post-critical regions. These can vary both with reflector location and from shot to shot.
Attempts to remove these artifacts involve time-consuming muting (setting to zero) of data in the sensor offset location and time domain, which is related in a non-linear, multi-value way to the reflection locations.